1. Field of the Invention
This invention relates to an electrical discharge machining machine. More specifically, it relates to a die milling electrical discharge machining machine in which the shape of the electrode is transferred to the work piece.
2. Description of the Prior Art
As is well-known, a die milling electrical discharge machining machine has a work table for the purpose of fixing the work pieces in plate, and also a work tank which surrounds the work table. In addition, a die milling electrical discharge machining machine has an electrode to perform electrical discharge machining and an electrode holder which is free to move along the X, Y and Z axes for adjustment.
In an electrical discharge machining machine with a configuration such as that described above, after the work piece is fixed in place on the work table the work tank is filled with enough working or dielectric fluid so that the work piece can be submerged in it. After that, the electrode is brought into contact with the top surface of the work piece, then the work piece is machined by moving the electrode in very small steps while an electrical discharge is produced between the electrode and the work piece.
In an electrical discharge machining machine as described above, kerosene is generally used as a working or dielectric fluid which satisfies the following conditions: (1) the molten metal filings produced by the electrical discharge machining are cooled and dispersed; (2) the dispersed filings are removed from the space between the work piece and the electrode; (3) parts which are heated by the electrical discharge machining are cooled; (4) the electrical insulation between the work piece and the electrode is restored. Sparks produced by the electrical discharge occur inside the dielectric fluid, and since there is no oxygen there is no danger of fire. However, if an electrical discharge should occur at the surface of the working or dielectric fluid because of an oversized work piece or a drop in the working or dielectric fluid level, there is a danger that the working or dielectric fluid will be ignited.
Therefore, in a die milling electrical discharge machining machine, the working or dielectric fluid level can be adjusted to correspond to the size of the work piece. In previous electrical discharge machining machines there was a level setting plate inside the work tank; the height of the plate could be adjusted directly to set the liquid level. This meant that the operator had to come into contact with the working or dielectric fluid and as a result the operator become soiled. In addition it was difficult to set the liquid level accurately.